


Fire Triangle

by MeGaLoTrash



Category: Undertale (Video Game)
Genre: Blow Jobs, Cunnilingus, Ecto-Penis (Undertale), Ecto-Tongue (Undertale), Ecto-Vagina (Undertale), Ectobiology, Explicit Language, Explicit Sexual Content, Fontcest, M/M, Multi, Papby, Papysansby, Restraints, Semi-Public Sex, Threesome - M/M/M, fire biology?, magical ones, maid uniform kink, more bad jokes, not canon but go with me on that one, sansby - Freeform
Language: English
Status: Completed
Published: 2017-07-27
Updated: 2017-07-27
Packaged: 2018-12-07 16:19:52
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,850
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11627259
Author URL: https://archiveofourown.org/users/MeGaLoTrash/pseuds/MeGaLoTrash
Summary: After witnessing the two Skelebros together, an over-worked Grillby jumps at the chance to spend more time with them.





	Fire Triangle

**Author's Note:**

> This is a sequel to my other fic 'Flaming' though it's not essential reading. Thanks for all the encouragement on that to write a follow up though!  
> Big thanks to @PastaU for letting me use their maid design as a reference.  
> shout out to @SesuRescue, together we will make the OT3 a thing ;)

Grillby went to lock up his bar as the sun was rising for the third time this week. He knew he should be taking a break. It had been a few weeks since his place on the surface had really kicked off, drawing both his old regulars and some braver humans. The unexpected surge and lack of fully trained staff meant he’d been working non stop. He moved from the door and staggered up the stairs leading to his flat above, throwing himself on the worn mattress as soon as he opened the door. He could have closed up on time, or trusted one of his trainees on a quieter night but he really wanted his bar to be a hit. Things were getting a little easier now though, and he promised himself he would have a night off this week. 

As he crawled under his bed sheets he couldn't help but think of what his friend had said about taking it easy. The smug skeleton had been trying to get him to take a night off ever since their… _encounter_. Grillby’s flames crackled around him as he let his thoughts stray to the skeleton brothers. This line of thought was becoming another repeat occurrence whenever he had a moment alone, but who could blame him after what he’d seen? 

Quite some time had passed since he had the privilege of witnessing them together, and he was itching for a repeat occurrence. It wasn’t intentional avoidance, he’d just been so busy with the bar..Sans had extended a few invites to hang out, but he understood when he had to decline. Grillby was a little worried though, he knew Sans was easy going but he didn't want to run the risk of hurting either of them with his refusals. If he had a choice he would have been there in a heartbeat. But because he was locking up late everyday he didn’t want to disturb them in the middle of the night. No matter how much he wanted to see them, life kept getting in the way.

It didn’t get in the way of his fantasies though. Grillby felt his hands come up to loosen his tie and fiddle with the shirt buttons while he re-lived the events of the costume party. _Sans and Papyrus showing up in matching outfits, fucking on his bar floor, Sans looking at him before he came_.... He noticed he was palming the front of his pants already just thinking about it. It was no secret that there had been tension between him and Sans for a long time, both of them being a bit of a flirt didn’t help matters. Grillby knew that Sans would never make a move on him though, he was completely in love with his brother and after getting over the initial shock of the taboo, Grillby could see they were perfect together. To be honest, since he found them both attractive he found the idea of them together erotic. Until recently he’d managed to keep his perversions to himself.

Grillby wasn’t shocked when they eventually got together, he was happy for them both. What had shocked him was the way Sans had started telling him in detail about their activities in the bedroom. It was almost as if Sans was scoping him out, and he found it hard to control his reaction as Sans teased him. Somehow he’d managed to arrange seeing his fantasies play out before him, Sans and his brother getting off on someone else watching them together. The image of them fucking on the floor of his bar was seared into his vision so much so he found it hard to walk past that spot without thinking about them entwined there 

Grillby unbuttoned his pants fully drawing out his member and sighing at the contact. However he made the mistake of glancing at his digital clock, groaning as it read 4.55am already. _I have to be up in 4 hours_. He sighed in frustration, rolling over and willing his magic to dissipate. It was just another thing he’d have to push back to a later date. Something had to change. 

 

It didn’t help his frustration when Sans sauntered into his bar the next day with a huge grin on his face. Grillby knew all too well what would have caused that expression. He tried to focus on setting out menus and keeping his magic under control, he didn’t want Sans teasing him on top of his internal monologue. _Sans and Papyrus, rutting together and moaning. A pair of hands extending to him, inviting..._. If Sans pushed him he would find it hard not to accept any invitation if it gave him the chance for more jerk off material. 

“hey grillbz wassup? you look beat man, been burning that candle at both ends?” Sans commented, hopping up onto his bar seat. Grillby tried not to respond to the terrible joke, but he had to admit he wasn’t wrong. He dreaded to think how bad he looked if it caused his constantly tired friend to comment. 

“You’re early” Grillby stated, trying to shift the attention of himself. He knew both Papyrus and Sans had jobs in a nearby city, so unless Sans had managed to wrangle an extended break it was odd to see him in the bar so early. 

“Yeah me and paps have a few days off, thought i’d treat myself to lunch” Sans twirled the menu between his phalanges, shifting in his seat. Grillby didn’t know why he bothered, he always had the same thing. And always covered lavishly in ketchup.

“I'll have the grillby sandwich” Sans had said pointing to the item on the menu. The grillby sandwich was a special he’d come up with involving chargrilled meats. Being made of fire was still a novelty for humans and he was enjoying capitalising on it. Though through all the years they’d been friends it was unlike Sans to try something new. Grillby pushed the feeling of him being up to something to the back of his mind as he left to cook his order. He knew he was probably imagining the feeling of being watched by Sans as he left for the kitchen.

 

“so erm grillbz… any chance you could finish early tonight?” Sans had finally piped up, halfway through his meal. Grillby and him had settled into an uncommon silence since he came back with the food and the skeleton’s behaviour was really throwing him off. The fact that the sandwich was covered in the red sauce had calmed him a bit but Sans seemed off, nervous even. Like he was hiding something. Grillby weighed up his options, he could brush him off again but he really didn’t want too. It was a weekday, it wasn’t too busy and he needed a night off. What tipped the scales was the desire to find out why his friend was so flustered.

“I can close about ten, why?” Grillby replied, adjusting his glasses and dropping his voice to mummer. He’d guessed that this conversation may turn private quite quickly. Sans shifted in his seat again, fumbling with his words. _something's really getting to him_ Grillby thought, his flames responding to his mind racing. 

“heh. well that’s great. see papyrus said he was gonna drop in later and erm, he said....jeez you think this would be easier now but-” Sans trailed off, clearly struggling with being clear. It was kind of endearing seeing his usually laid back friend get a little flustered. Grillby laid a hand over his friend’s arm, keen to reassure him he was interested even if he had been absent.

“It's fine Sans, what does he want?” he let his hand drift up the others arm when he spoke. No one was watching and honestly he was starved of an affectionate touch. He knew Sans would stop him if he crossed a line, but he made no move to.

“that's the thing grillbz he won't tell me. something about switching it up a bit. he’s asked me to ask you if you would want to… join us.” Sans eventually confessed. His meal had long been forgotten, he seemed content to focus on the flames licking up his arm now Grillby’s energy was crackling more wildly. Watching them both was one thing, but getting the chance to join in? Grillby could hardly contain himself as desire rippled through his body. He’d be lying if he hadn’t been waiting to hear Sans ask him for years, and the crush he had on his younger brother was fast developing in intensity. _And they both wanted him?! … Fuck_

“I do” he replied, clinging on to the last shreds of his control. He wanted to tell Sans how much he’d been thinking about fucking them both. How they were always on his mind. How often he touched himself reliving that night over and over. 

“ i'll let him know you’re in. sorry i don’t have too many details but he's told me to stay here and he'll join us at closing time. oh and he said to keep the back door unlocked” sans offered a small smile. He drew his arm away quickly and nodded towards a couple at the bar waiting for service. Grillby tried his best to snap back to his hosting role but didn’t miss Sans pulling out his phone and sending a message sealing the plans for the evening.

The rest of the day went by in a haze for Grillby. The combination of over-tiredness, trying to organise an early close, and an ever pressing arousal kept making him lose focus. Sans was little help, splitting his time between tittering at his phone and looking at Grillby with a lecherous gaze. He was pretty sure he was plotting with Papyrus. _What had he got himself into?_. Sans did help him move stuff when it came time to close up, helping him to stack up the chairs after he locked them in. They got to talking and Sans was telling him an elaborate story about a prank he’d been pulling on his colleges involving his use of ‘shortcuts’. He found himself laughing along as the skeleton described in detail about how one of the humans had started watching security cameras to catch him out. 

Grillby had been so caught up in his friend's story that he hadn't noticed someone come up behind him before it was too late. He saw two magical blue bones crossing in front of him trapping him between them and the solid figure behind him.

sp

“Hello Grillby... Sans Has Told Me You’ve Been Working Too Hard” Papyrus spoke behind him. Grillby was completely thrown off, this low seductive tone coming from Papyrus being totally out of character. He could tell he wasn’t the only one affected. Sans’s expression had completely changed; his eye lights were almost gone as he was frozen on the spot. 

“I Know Sans Has Asked Your Permission To Join Us, I Just Want To Make Sure. Do You Want This?” Papyrus Leant further into him as he spoke, making sure to let his breath ghost over his neck. The change in temperature and air pressure made Grillby shudder. His flames had begun flicker around his captor’s frame, his body making a decision before his mind had chance to catch up. Still he knew Papyrus would never act without express permission, he gathered his thoughts and tried to stay calm as he uttered a shaky reply. 

“I do” 

As soon as the words had left his lips Papyrus began his assault. The skeleton kept the bone attacks up, magically trapping them together as he began grazing his teeth against the flames on his neck. Grillby felt boney hands pull at his own and he allowed himself to be guided as he gave into the sensations. A quick glance at Sans showed his eyes were almost back to normal if a bit hazy. His expression was perverted, dragging his tongue over his teeth purposefully while watching them both. 

When his hands were behind him Grillby felt something seal over them, essentially binding them in place behind them. He moved against his bindings only they were stuck firmly, most likely made of the same magic as the bone constructs. His mind raced wondering _how_ Papyrus could have managed to make them, or why he’d spent the time learning. He heard a giddy laugh from Papyrus as he moved in front of him, dispelling the bone attacks and leaving him stood swaying to re-center his balance. 

“Had To Improvise, You Would Have Burned Through Our Metal Ones. I Think It’s Time We Help You Relax. I Want You To Let Go” Papyrus had carried on walking until he was stood in facing him, and Grillby finally had a view of what he was wearing. _No wonder Sans was being such a perv_. Grillby felt his flames flicker erratically as he took in the sight of Papyrus wearing an outfit straight out of a wet-dream. 

Papyrus had somehow managed to get a hold of barmaid outfit, and a decent one at that. It consisted of a high necked, long sleeved, black shirt with a frilly white collar piece and bow. It actually looked perfectly respectable from the waist up. However the bottom half was straight out of a kinky fantasy. The black skirt and apron were short to begin with, but it was made worse with the frilly underskirt fanning out making it ride up Papyrus’s legs. His ecto-body was already formed and helping to hold up a pair of suspenders that made Grillby wonder where the hell he’d managed to find something so perfect. He even had a maid’s hat to top it off. When Papyrus realised he was being stared at he gave them both a little twirl, enjoying the attention.

“fuck pap, you look good” Sans piped up, saying what they were both thinking. His eyes had practically turned to hearts as he swooned over his lover, most likely getting just as good a view from behind. Grillby wondered if Papyrus was even wearing panties. 

“Language Brother! Don't Make Me Restrain You Too” Papyrus warned, his hands glowing as he threatened to form an attack. 

“Fuck cunt piss shit ah-” Sans brought it on himself but grillby couldn't believe the speed in which papyrus moved from his position in front of him to behind Sans. Papyrus Pinned his brother’s arms behind his back in one swift motion, catching him off guard. Papyrus may have looked sweet in his outfit, but there was no arguing over who was currently in charge. 

“oh my god pap ahh-” Sans cried out as his wrists got the same treatment. A construct of binding blue magic held them shut as papyrus held him back roughly. 

“ I wasn’t planning on this but-” Papyrus kept one hand on his brother’s back but brought the other around to begin stroking his ribs. “-since your both tied up, i have a few things to ask” 

Sans gasped at the touch, the light blush dusting his cheeks darkening. The material of Sans’s shirt had ridden up and somehow seeing exposed bone made him look more vulnerable. Grillby wondered if this was the first time he’d ever been in such a submissive position. Sans had been in the driving seat last time, so he had assumed that was their natural dynamic. The way Sans shivered until his brother’s light touches, pressing into the taller body behind him seemed to surprise even him. Grillby could feel himself get carried away with watching them both again, his arousal forming a tent in his work pants.

“So You Like Watching Us, Grillby?” Papyrus broke the silence. From what Grillby could tell he’d been observing him while turning Sans into Putty. He couldn’t deny it, he felt a wave of shame threaten to creep up on him over being caught again. _What had Papyrus Said about letting go?_. Grillby was in safe hands, with people he wanted. He needed to stop over-thinking and live in the moment. 

“ ...Yes” 

“Tell me, is it just watching us or-” Papyrus pulled down the front of his brothers shorts, exposing his thick blue member to them both “- do you think about fucking my brother’s cock.”

“Both” Grillby replied, a little too eagerly for his own comfort. _No point in holding back now_. He found himself more than willing to follow Papyrus’s lead, he could feel the anxious energy leaving him as he no longer had to worry about making decisions. Being magically bound was strangling comforting. 

“Good. Suck Him Off” Papyrus commanded, the hand he’d used to pull down his brother’s shorts worked his length up and down in a few teasing strokes. Sans managed to turn a darker shade of blue as he looked up at his friend with a nervous expression. Grillby couldn’t deny he was really liking where this little game was going.

Grillby moved forward tentatively, well aware of two sets of eye lights watching him intently. Dropping to his knees was a little harder with his hands bound, making him come down a little closer than he originally intended. The ecto-flesh in front of him was already leaking at the tip, the liquid a slightly brighter shade than the cock it was coming out of. Papyrus used his hand to guide his brother’s length towards Grillby, he quickly parted his flames allowing his mouth to form. 

Grillby felt Sans rest his tip just outside his mouth and he gave his friend a moment to adjust to the temperature change before taking him all in. He may have seemed like the quiet type but Grillby had picked up a few tricks from his bar in the underground. He’d been waiting to do this for too long and he was set on making his friend feel amazing. His hot tongue played with the underside of Sans’s cock as he hollowed his cheeks, providing suction down to his base. Grillby raised his eyes looking up at them both over his glasses, well aware of the effects of that look. Sans was panting now, attempting to write against Papyrus’s firm grasp. Papyrus was focused on where they were joined, his eyes lit up in wonder and looking a little more like his usual ‘innocent’ self. The contrast was delicious. 

“shit, it’s so warm. fuck ah-” Sans cried out, bucking his hips when his brother decided to give his spine a firm stroke. Grillby had no idea their bones could be so sensitive given the right touches, and he mentally filed that information away for later. He wanted to let his hands roam all over both of them, finding their most sensitive points and dragging his flames over them. But for now, he was more than happy to be working the thick cock in and out of his mouth. Sans tasted a lot sweeter than he thought he would, but there was a distinct tangy aftertaste. Grillby had no idea ecto flesh had a taste, and he found himself sucking harder wanting more.

Sans was quickly becoming a mess. Between Grillby’s mouth and Papyrus’s practiced touches he was a twitching mess. If given the chance Sans would probably be writhing around a lot more but Papyrus had made sure to trap him between them. Sans’s bound hands pulled at Papyrus’s skirt in a fist but his face was one of complete bliss. It seemed like Grillby wasn’t the only one in need of letting go. He upped the ante slightly, humming around the length in his mouth, enjoying the increased volume of moans. Grillby got so caught up in the moment it took him a moment to realise his shoulder was being tapped lightly. 

“I’d Stop, He’s Getting Close” Papyrus instructed. 

Grillby removed himself from Sans with an audible pop while Papyrus let him down to the floor easily, all too aware of his brother’s legs turning to jelly. Sans face ended up inches away from Grillby’s own and he found himself leaning in before he had time to think. The contrast of his flames and the hard bone of bare teeth was interesting, but his mouth being invaded by the others tongue felt amazing. He felt his the bindings around his hands loosen and moved his hands to grab at the other’s skull depending the kiss. Grillby felt Papyrus move around them both and used his new freedom to drag him downwards, swapping over to pull him into a kiss. 

“Wowie That Was Really Fun To Watch, But I Want More. Sit On His Lap, Grillby” Papyrus had panted pulling away. Both Grillby and Sans were a little put out by this suggestion, surprised Papyrus wasn’t getting more involved. _maybe he wasn’t the only one who liked watching_

“pap, you sure you're ok with that?” Sans asked, concern for his brother momentarily winning over his arousal.

“Of course sans! I Get To Watch You Fuck Him, Then I’m Going To Sit In His Lap And Ride Him.” Papyrus was practically beaming. Grillby felt the last of his reservations disappear. With a proposition like that, how could he refuse?

“It will be the perfect Grillby sandwich” Papyrus winked and Sans sniggered. _Fuck_ he should have seen that coming when Sans had ordered food earlier. They really were starting to rub of on each other if the bad jokes were anything to go by. Grillby covered his face in his hands and groaned before being pulled over by Sans, his hands having been released as well.

“do you need to be prepped?” Sans whispered, managing to turn the charm back on instantaneously.

“No its magic but-” Grillby trailed off, hesitating. Magic was a lot more accommodating than physical flesh so he didn’t need to be stretched out. But the idea of bony fingers fucking him had 

“you'll enjoy the feeling? I hear you loud and clear grillbz” Sans finished his thought for him. 

Grillby got to work in removing his pants, his erection bobbing free in the process. He wasn’t as thick as Sans but probably stood a little longer, the flame magic making it up swirled excitedly around the solid form. He straddled Sans’s waist kneeling and facing away. He wanted to make the transition from fingers to sliding on his friend’s cock to be as quick as possible, and this position meant Papyrus could join whenever he was ready. He felt a solid digit tease at his entrance as an idea crossed his mind. He made eye contact with the taller skeleton as his brother’s finger entered him and he couldn’t hold back a moan. 

“Papyrus come here-ah! I'll need to get you used to the heat too” Grillby motioned him over trying to keep some form of composure while feeling hard bone slipping further inside him. 

Papyrus looked more than eager to oblige coming towards them and lifting. With one hand still bracing himself on the floor he used his free hand to push the rest of Papyrus’s skirt out of the way. Turns out he wasn’t wearing panties after all. With his hand occupied in keeping the other’s skirt held up he opted instead to lean in and lick over the dripping slit. Papyrus reacted instantly to the temperature change, the heat of his magical tongue contrasting the cooler ecto-flesh. Sans Had Slipped a second finger into him now and was practically growling praise over his shoulder. 

Grillby used his tongue to explore all around his folds, enjoying the little whimpers and cries Papyrus couldn’t hold back. He found himself arching into Sans now, The hard phalanges working him up till he was moaning into Papyrus. The taller skeleton didn’t seem to mind, the vibrations almost making him lose his footing. Grillby heard Sans curse under his breath behind him before removing his fingers and lining himself up. The change in texture was evident, and Sans was A lot bigger than two of his fingers. The stretch was overwhelming as Grillby felt Sans Slide in, causing him to break from Papyrus and arch his head back with a cry. Sans stopped suddenly and concern came over the brother’s over Grillby’s reaction. 

“It's fine. It’s just - You’re pretty big” Grillby reassured them, adjusting his position slightly and causing Sans’s breath to hitch. 

“heh - way to stroke a guy’s ego grillbz, it's ok take your time” Sans’s voice was strained, the heat wrapping around him feeling amazing.

Sans stilled inside him, giving Grillby the chance to adjust fully and take his lead. Grillby buried his face back between Papyrus’s legs, dipping his tongue inside the other’s entrance. He allowed his hips to move at a slow pace, grinding himself on Sans’s cock and drawing him in and out slowly Grillby felt hands come to grip his hips as Sans gave into the sensations and bucked against him. 

Papyrus moved on top of him now, long legs straddling them both causing Grillby to sink deeper on top of Sans. Grillby used both of his hands to guide Papyrus’s hips down onto his length. The feel of the other’s magic pussy taking him in felt amazing, he found it hard not to push himself all the way in at once. He distracted himself by running his hands up underneath the skirt, delighting in how Papyrus could look so adorable and Lewd at the same time. 

“fuck this is hot, literally.” Sans increased his pace slightly now papyrus was fully seated on top of Grillby. The movement Sans thrusting into him made him move up into Papyrus and it didn't take too long for them to find a rhythm. 

 

Grillby had on of his hands trailing over the flesh of Papyrus's inner thigh and he was fascinated by how sensitive it was to his touch. Papyrus had pulled his skirt up further around his waist now, leaning back on the other giving both Grillby and Sans a great view. Grillby could see how the other’s magical flesh, while solid, was also semi transparent. He could actually see his cock thrusting up inside him. 

The feeling of being both filled and being buried inside someone at the same time was indescribable, and better than any of Grillby’s fantasies. He could feel his magic begin to crackle violently around them all and it just seemed to spur his two partners on. His usual quiet and reserved mask was forgotten, and he allowed himself to moan fully now. Papyrus was just as vocal, he had his eye sockets closed tightly as he fucked himself on Grillby’s cock. Sans’s moans were more guttural and littered with curses which sent shivers up his body.

Grillby felt Sans shift his hips and strike at an angle that had him seeing stars. Knowing he wouldn’t be able to last much longer Grillby moved on of his hands to circle the bundle of nerves at the top of Papyrus’s pussy. He felt him tighten around his length and buck against him faster as he approached climaxed. Sans Thrusts became harder and on another brush against his sensitive spot Grillby felt himself topple over the edge. 

His cum shot up into Papyrus, breaching the top of his magic and sending spurts up over his ribcage. The feeling of such a hot substance hitting bare bone must have done it for Papyrus. He seated himself fully before crying out, his walls fluttering and prolonging Grillby’s release. Sans thrust twice more before hilting himself and cumming hard. Grillby felt the contrast in temperature go the other way with the ecto-plasmic cum on his sensitive insides. He cried out one last time shuddering against them, he felt incredible wedged between the two brothers. 

 

“you’d think none of us owned beds with the amount of times we've fucked on this floor” Sans decided to break the comfortable silence between them, continuing to run his phalanges up Grillby’s sides. 

 

“Sans! Besides the hard surface is good for your bones” Papyrus moved off him first, straightening his maid skirt as if nothing had happened and extending a hand to help Grillby up. He accepted, Carefully removing himself from Sans before standing and wrapping his arms around Papyrus in a playful embrace. 

“I’ve heard heat is better for sore joints” Grillby commented, surprising the others with his innuendo. 

Sans had come up behind him to join the hug and he could feel the other laughing against him as Papyrus feigned annoyance. In truth he was enjoying snuggling into them both, and returned the hug enthusiastically, planting a skeleton kiss on Grillby’s cheek.

“I Know Its Too Late For Dinner, But What About Staying Over At Our House Tonight Grillby? I’ll Make Breakfast Instead!” Papyrus beamed at him. Any worry Grillby had over this becoming awkward between them was gone with how at peace he felt between them. Sans had grabbed his pants and was handing them to him with a smile across his face. Both brothers seemed intent on having him come over still even after what had just happened. How could he refuse?

**Author's Note:**

> thankyou for reading! hope you enjoy!


End file.
